1. Field of the Invention
The present invention relates to semiconductor devices and manufacturing methods thereof, and more particularly, to a manufacturing method of a semiconductor device which ensures a good electrical connection of metal interconnections, and a semiconductor device obtained by the mentioned manufacturing method.
2. Description of the Background Art
In recent years, as semiconductor devices represented by ULSIs have become more integrated and more powerful, complexity and density of structures especially interposed in the vertical direction between metal interconnections have been increasing. A conventional method of manufacturing a semiconductor device having metal interconnections will now be described by way of example.
Referring first to FIG. 32, a polycrystalline silicon (hereinafter, referred to as xe2x80x9cpolysiliconxe2x80x9d) plug 104 is formed on a semiconductor substrate (not shown). A silicon oxide film 103 is formed on the semiconductor substrate to cover polysilicon plug 104. A prescribed photo resist pattern (not shown) is formed on silicon oxide film 103.
Using the photo resist pattern as a mask, silicon oxide film 103 is subjected to anisotropic etching to form a contact hole 105 exposing the surface of polysilicon plug 104. The photo resist pattern is then removed.
Next, a barrier metal 106 including a titanium nitride film is formed by sputtering. At this time, barrier metal 106 formed on the upper surface of silicon oxide film 103 and on the side and bottom surfaces of contact hole 105 has approximately the same film thickness ti.
Next, a metal film 107 including tungsten is formed by sputtering or the like to cover barrier metal 106. A prescribed photo resist pattern 132 is formed on metal film 107.
Referring next to FIG. 33, metal film 107 is subjected to anisotropic etching using photo resist pattern 132 as a mask, to expose the surface of barrier metal 106 located on the upper surface of silicon oxide film 103.
Referring next to FIG. 34, the exposed barrier metal 106 is further anisotropically etched using photo resist pattern 132 as a mask, so that the upper surface of silicon oxide film 103 is exposed. Thereafter, photo resist pattern 132 is removed. A metal interconnection 107a is thus formed from metal film 107.
Next, an interlayer insulating film (not shown) is further formed on silicon oxide film 103 to cover metal interconnection 107a. Accordingly, a main portion of the semiconductor device having the metal interconnection is completed.
The above-described method of manufacturing a semiconductor device, however, exhibits the following problems. At the step shown in FIG. 34, after the etching of barrier metal 106 for the film thickness ti, over-etching is conducted such that no etch residue of barrier metal 106 is left on the upper surface of silicon oxide film 103.
This over-etching may cause barrier metal 106 located on the side surface of contact hole 105 to be etched away, which leads to exposure of the surface of polysilicon plug 104. Thereafter, the semiconductor substrate is processed with HCl or NH4OH to remove metal contamination or dust particles thereon.
At this time, if the cleaning with NH4OH is performed with the surface of polysilicon plug 104 being exposed, isotropic etching will proceed from the exposed portion of polysilicon plug 104 as shown in FIG. 35, so that a concave portion 120 is formed. If the interlayer insulating film (not shown) is formed in this situation, the concave portion 120 will become a void.
This void may cause an unstable electrical connection between metal interconnection 107a, barrier metal 106 and polysilicon plug 104. Further, metal interconnection 107a and barrier metal 106 may be disconnected from polysilicon plug 104. As a result, the operation of the semiconductor device would become unstable, hindering a desired operation.
The present invention is directed to solve the above problems. One object of the present invention is to provide a manufacturing method of a semiconductor device having metal interconnections ensuring a stable electrical connection. Another object of the present invention is to provide a semiconductor device obtained by such a manufacturing method.
A manufacturing method of a semiconductor device according to a first aspect of the present invention includes the following steps: the step of forming a conductive region on a semiconductor substrate; the step of forming an insulating film on the semiconductor substrate to cover the conductive region; the step of forming a hole in the insulating film to expose a surface of the conductive region; the step of forming a conductive layer in the hole, that is electrically connected to the conductive region exposed at the bottom of the hole; and the step of forming a conductive portion by etching the conductive layer. At the step of forming the conductive portion, an etch rate of the conductive layer is set smaller at least in the vicinity of the side surface of the open end of the hole than in the other portion, to prevent the exposure of the surface of the conductive region at the bottom of the hole.
According to this manufacturing method, at the step of forming the conductive portion, the exposure of the surface of the conductive region at the bottom of the hole is prevented particularly taking advantage of an RIE-lag effect. Thus, even if processing with NH4OH is conducted in a later step for removal of metal contamination or dust particles on the semiconductor substrate, the conductive region is prevented from being etched. As a result, it is possible to accomplish a semiconductor device in which a good electrical connection between the conductive portion and the conductive region is ensured. The RIE-lag effect will be described below in conjunction with embodiments of the present invention.
Preferably, the step of forming the conductive layer includes: the step of forming a first conductive layer having a film thickness smaller on the side surface of the hole than on the upper surface of the insulating film or on the bottom surface of the hole; and the step of forming a second conductive layer having an etch characteristic different from that of the first conductive layer, to cover the first conductive layer. The step of forming the conductive portion preferably includes: the step of forming a mask material, on the second conductive layer, having a diameter smaller than the aperture of the hole at its open end; the step of anisotropically etching the second conductive layer using the mask material as a mask, to expose the surface of the first conductive layer located on the upper surface of the insulating film; and the step of further anisotropically etching the exposed first conductive layer using the mask material as a mask, to remove the first conductive layer located on the upper surface of the insulating film and the first conductive layer located between the side surface of the hole and the second conductive layer.
In this case, when the first conductive layer located between the side surface of the hole and the second conductive layer is subjected to etching, the first conductive layer formed on the side surface of the hole is thinner than the first conductive layer formed in the other portions. This prevents sufficient etchant from entering the narrow portion as the etching proceeds, so that the etch rate of the first conductive layer in this portion becomes smaller than that in the other portions. Accordingly, at the time of anisotropic etching of the first conductive layer, it is possible to reliably prevent the exposure of the conductive region even if over-etching is conducted.
Preferably, the step of forming the hole includes the step of shaping the hole such that the hole has a bowing or upwardly tapering cross section.
In this case, the first conductive layer can readily be formed by sputtering, for example, to have a film thickness smaller on the side surface of the hole than in the other portion.
Preferably, the step of forming the hole includes the step of setting an aspect ratio of the hole to at least 0.75.
Again in this case, the first conductive layer can readily be formed by sputtering, for example, with a film thickness smaller on the side surface of the hole than in the other portion.
The manufacturing method of the semiconductor device according to a second aspect of the present invention includes: the step of forming a conductive region on a semiconductor substrate; the step of forming an insulating film on the semiconductor substrate to cover the conductive region; the step of forming a hole in the insulating film to expose the surface of the conductive region; the step of forming a conductive layer in the hole, that is electrically connected to the conductive region exposed at the bottom of the hole; the step of forming a conductive portion by etching the conductive layer to remove a portion of the conductive layer in the vicinity of the side surface of the hole from its open end down to its bottom; and the step of forming an etch stopper layer having an etch characteristic different from that of the conductive region, in a region at the bottom of the hole between the conductive portion and the side surface of the hole that is at least exposed by removing the conductive layer at the step of forming the conductive portion.
According to the manufacturing method as described above, when etching the conductive layer at the step of forming the conductive portion, even if the bottom of the hole is exposed by over-etching, there exists the etch stopper film at the exposed portion. Thus, even if a processing with NH4OH is performed in a later step for removal of metal contamination or dust particles on the semiconductor substrate, the etch stopper film protects the conductive region, preventing the conductive region from being etched. As a result, a semiconductor device ensuring an electrical connection between the conductive portion and the conductive region is accomplished.
In the case where the conductive region includes a polysilicon film, a metal silicide layer is preferably formed as the etch stopper film, by causing the silicon within the conductive region to react with metal.
Alternatively, a silicon oxide film may be formed as the etch stopper film by oxidizing the silicon on the surface of the conductive region exposed after the formation of the conductive portion.
For the oxidization of the silicon in the conductive region, the exposed surface of the conductive region is preferably brought in plasma atmosphere including oxygen.
The manufacturing method of a semiconductor device according to the third aspect of the present invention includes the following steps: the step of forming a conductive region on a semiconductor substrate; the step of forming an insulating film on the semiconductor substrate to cover the conductive region; the step of forming a hole in the insulating film to expose the surface of the conductive region; the step of forming a conductive layer in the hole, that is electrically connected to the conductive region exposed at the bottom of the hole; and the step of forming a conductive portion by etching the conductive layer. The step of forming the conductive layer includes: the step of forming a first conductive layer; and the step of forming, on the first conductive layer, a second conductive layer having an etch characteristic different from the etch characteristic of the first conductive layer. The step of forming the conductive portion includes: the step of forming a resist pattern on the second conductive layer to entirely cover the open end of the hole; and the step of anisotropically etching the second and the first conductive layers using the resist pattern as a mask.
According to the manufacturing method as described above, the resist pattern for the formation of the conductive portion covers the entire open end of the hole. Thus, during the etching of the second and first conductive layers, the layers located in the hole are not etched away, hindering the exposure of the bottom of the hole. Therefore, even if a processing with NH4OH is performed in a later step for removal of metal contamination or dust particles on the semiconductor substrate, the conductive region is prevented from being etched. As a result, a semiconductor device ensuring an electrical connection between the conductive portion and the conductive region is achieved.
The semiconductor device according to the fourth aspect of the present invention includes: a semiconductor substrate, a conductive region, an insulating film, a hole, and a conductive portion. The semiconductor substrate has a main surface. The conductive region is formed on the semiconductor substrate. The insulating film is formed on the semiconductor substrate to cover the conductive region. The hole is formed in the insulating film, exposing the surface of the conductive region. The conductive portion is formed in the hole, and electrically connected to the conductive region exposed at the bottom of the hole. The conductive portion has a portion spaced apart from the side surface of the hole at least in the vicinity of the open end of the hole.
This semiconductor device is obtained by the manufacturing method of a semiconductor device according to the first aspect of the present invention. During the formation of the conductive portion, the conductive layer in the vicinity of the side surface of the hole is being etched. As the etching proceeds, however, the RIE-lag effect prevents the etchant from entering the etched portion, thereby avoiding the exposure of the conductive region located at the bottom of the hole. Accordingly, the conductive layer is etched in the vicinity of the open end of the hole, where the side surface of the hole is exposed. The conductive portion thus has a portion spaced apart from the side surface of the hole.
The hole preferably has its open end narrower than its inner opening portion. Specifically, it is further preferred that the hole has a bowing or upwardly tapering cross section.
As explained above, a prescribed conductive layer constituting the conductive portion can readily be formed to have a film thickness smaller on the side surface of the hole than on the bottom surface of the hole or on the upper surface of the insulating film.
Preferably, the conductive portion has a portion spaced apart from the side surface of the hole from the open end of the hole along the side surface of the hole. Further, it is preferred that a prescribed layer having an etch characteristic different from that of the conductive region is formed at the bottom surface of the hole located between the conductive portion and the side surface of the hole.
This semiconductor device is obtained by the manufacturing method of a semiconductor device according to the second aspect of the present invention. The prescribed layer having the etch characteristic different from that of the conductive region is formed at the bottom of the hole, at least at a portion where the conductive region is exposed when forming the conductive portion. This prescribed layer protects the conductive region, preventing the conductive region from being etched during the processing with NH4OH in a later step.
The conductive region preferably includes a polysilicon film. The prescribed layer preferably includes a metal silicide layer, or it may include a silicon oxide film.
The semiconductor device according to the fifth aspect of the present invention includes: a semiconductor substrate, a conductive region, an insulating film, a hole, and a conductive portion. The semiconductor substrate has a main surface. The conductive region is formed on the semiconductor substrate. The insulating film is formed on the semiconductor substrate to cover the conductive region. The hole is formed in the insulating film to expose the surface of the conductive region. The conductive portion is formed in the hole, and electrically connected to the conductive region exposed at the bottom of the hole. The conductive portion has a first conductive layer and a second conductive layer, formed on the first conductive layer, having an etch characteristic different from that of the first conductive layer. The second conductive layer is formed to entirely cover the open end of the hole.
This semiconductor device is obtained by the manufacturing method according to the third aspect of the present invention. The resist pattern for the formation of the conductive portion is formed to cover the entire open end of the hole, so that the second conductive layer being etched using the resist pattern as a mask entirely covers the open end of the hole.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.